Firing means



NOV- 19, 1945- H. J. RoLFEs ET AL 2,4L339 FIRING MEANS Filed Dec. 16, 1942 Patented Nov. 19, 1946 nrimNef MEANS Hans .lay Rolfes, `Melrose,-'1`ransvaal, and Eric. i

Cliffordllalliday, Parktown North, Transvaal,- Union of'South Africa Y Application Decemberlf, 1942 SerialrNo. 469,244 :il Inthe Union of South AfricaSeptember 25, 1941 v1 claim. f (C1. 1oz-f2s) This invention relates gto rneansffor safeguardearthbut leavesa residual chargein'oneilead or ing-,the electricfigniters of blasting detonators theA other, no` now of currentin the igniter orig-` against accidental' ringby electric currents or niters suilicient to `set offthellatter, will result.

spark discharges produced respectively in, or in As will be appreciated, the self-inductance the vicinity or, the iiring means of the igniter by meanslshould beas smallindmensions as is conatmospheric electricity. sistent with its capability ofproducing the req- Itfisobvious that a possible solution to this uisite choking. effect- Preferably, therefore, the

problem isto surround thef two electricY leads of self-inductance means comprises a continuous the igniterat a position ia-saferdistanee from the soft iron or other magnetic ocre in the form of ring meansthereof by` an earthed mass of a maan oval link, ring, or the like on 'opposite halves terial; whichgwill exhibit ahigh resistance at voltn of which the igniter or blasting circuit leads (enages of the magnitude used fqriintentionally nrclosed in their usual insulated covering) are ing the igniter and a low resistance at voltages woundl 1@or the samerea'son, the one leady inthe of Vthe magnitude of the electrostatic charges case vjust-mentioned isvvoundinthe form of a which produce the currents and spark discharges right-hand fhelix and the .f other in a left-hand aforesaid. helix, so 'that theinductancesof thetwo helices One means of obtaining a solution of the probor coils add together. lem 1in the Vmannerjustindicatedis described in vThree embodiments of 4the invention will novv the Yzzo-,pendingPatent,Application No. 455,235, lee-described, by'way of example, with reference now Patent 2,403,125, viz. to Aemploy a material to theannexed-drawing, in which:

which oers av complete or substan-tially com- Fig. l is-a sectional elevation of a combined-lilplete resistanceto voltages oi the'magnitude used termeans andself-inductance means enclosed in for intentionally ringthe Vigniter and which, on afiseparatel casing.

its being subjected to voltages of the magnitude Fig-2 is an elevation, partly in section, of a selfof, electrostatic Charges caused by atmospheric 25 inductance. means enclosed in a container with a electricity, becomes locally conductive through ltel means and detonator.

coherer; action along a path or paths permitting FigfS is a diagrammatic View of a self-'inductthe kpassage therethrough of the high voltage ance means and lter meansapplied to a b1ast- Charge, ing circuit including a groupof detonators.

In any Solution .as above, itis important that Referrngrto 1 the drawing.:

thepath' V01 :paths to earth aiorded by the mass In the embodimentshownin Fig. 1, the self-im of material (which will hereinafter be referred to dllCaTlCe means COIISiStS 0f a Soft-iron oval core as the lter means) to high voltage charges l which is elongated in the direction of its enshould be such as to ensure that as far as possi- ClOSYlg Coppel' Casing 2 S0 aS 150 ft neatly thereble, the whole charge passes instantaneously to n- OIl the ODDOSte halves 0f the @Ore the i11- earth, without leaving any residual charge in one Sllated igniter leads 3, 4 are WOlmd, the lead 3 lead or the other capable of producing a now of being Wound on the left-hand half of the core in current in the ring means, e. g. bridge-wire, sufthe fOIm 0f a right-hand helX 3a and the lead 4 ficient to heat the latter to incandescence. It being wound on the right-hand half in the form may not be possible, however, to discharge the 40 of a left-hand helix 4a, so that the inductances whole of the high voltage charge through the il- 0f the GWG helices add Ogei'fhel.

ter means to earth in every case, e. g. in the case The 10We1 ends 3b, 4b 0f the leads 3, 4 are 60nof exceptionally heavy charges or charges of exnected to the igniter (not shown) and on the side ceptionally high voltage. of the inductive helices 3a, ila remote from these According to the invention we provide, in com.. ends, the leads 3, 4 are bared for a short distance bination with a filter means as aforesaid, a selfet parts 3c, 4 and SU-II'Oullded by a lter means inductance means located in the igniter or blast- 5. This means may C0nsst 0f any earthed mass ing circuit leads between the filter means and the 0f vmaterial which will exhibit, as aforesaid, a igniter or igniters, whereby flow of current high resistance at voltages of the magnitude used caused in one lead or another by atmospheric for intentionally ring the igniter and a low reelectricity is choked back or prevented from vsistance at voltages of the magnitude of the elecreaching or setting off the igniter or igniters, In trostatic charges induced by atmospheric elecparticular, the self-inductance means ensures tricity. For example, the filter means 5 may be that, even in cases in which the whole of the high a coherer plug as described in the co-pending voltage charge does not pass instantaneously to Patent Application No, 455,235, now Patent 2,408,125, and the leads 3, 4 may, Whatever be the filter means used, be provided or associated with discharge points to promote or facilitate the discharge of the high voltage charge from the leads or either of them into the earthed mass; e. g, discharge points constituted by outwardly directed teeth 3d, 4d are formed on the bared parts 3C, 4c of the leads 3, 4 within the filter mass 5 shown in Fig. 1.

The casing 2 is closed at the ends by rubber plugs 6, 'I or other sealing means secured in place by crimping 8, 9 at the said ends, and a rubber plug or other sealing means I is provided between the lter mass and core I.

With the means illustrated, high voltage electrostatic charges induced in the lead 3 and/or lead 4 will normally be discharged wholly and instantaneously through the discharge points 3d and/or discharge points 4d, and thence through the filter mass 5 and the copper casing 2 to earth. Any tendency for the high voltage charge to pass down the lead 3 and/or lead 4 t0 the igniter is prevented by the choking effect of the inductance means I, 3a and 4a. Thus, even in the case of exceptionally heavy charges, or charges of exceptionally high Voltage, which might otherwise leave a residual charge in one lead or the other, no ow of current takes place through the lead 3 or 4 to the firing means or bridge-wire suicient to set off the igniter.

In the embodiment illustrated in Fig. 2, the inductance means consists of a soft-iron link or core I I around which the leads 3, 4 are wound in the form of right and left hand helices 3a and 4a respectively. The inductance means is located Within an aluminium container I2 which also contains the lter means 5 and a detonator I3 (which latter may be of any known type, e. g. instantaneous, Eschbach, or provided With a separate igniter and intervening exible fuze) The lter means 5 is adapted to be earthed, e. g. by copper Wire I4 wound round the copper casing of the detonator I3 and also connected if desired, as shown diagrammatically at the points I 5, to the interior of the container I2. In function, as will be appreciated, the filter and inductance means Shown in Fig. 2 are similar to those described with reference to Fig. 1.

Fig. 3 shows the application of the invention to the protection of a group of detonators I6. The leads II, IB of the blasting circuit are wound re- `means may be applied similarly to the circuit of a parallel-connected group of detonators.

By this use of a self-inductance means in the leads of the blasting circuit, the necessity for separate self-inductance means in the leads 2|, 22 (Fig. 3) of the individual detonators I 6 can be avoided.

As the result of experiment it has been determined that the self-inductance means should preferably have as a minimum a self-inductance of 30 milli-henries or thereabout, i. e. 15 millihenries or thereabout in each lead.

If desired, the magnetic core may be made flexible to some degree, e. g. by building up lthe same from a length or strands of thin soft iron wire.

It is to be understood that in the appended claim the term igniter leads is intended to i11- clude the leads of either an individual ignter or the leads of a group of series-connected or parallel-connected igniters, and that by the term filter means we signify a lter means as hereinbefore referred to.

We claim:

In a blasting unit, electrically-responsive firing means, electric leads serving such means, a primary safeguarding means in electrical contact with such leads and electrically inert to normal voltage ring charge through said leads and fully conductive to current flow from said leads of an abnormal voltage current throughsaid leads, and a secondary safeguarding means between the ignition means and said primary means, said secondary means being within the electrical influence of the leads and preventing flow through said leads to the ignition means of residual or like current flow uncontrolled by the primary means, said secondary means including a magnetic core on which the leads are Wound in relatively-reversed helix form respectively.

HANS JAY ROLFES. ERIC CLIFFORD HALLIDAY. 

